<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>后代选择器</title>
  <style>
    div span {
        color: red;
    }
  </style>
</head>
<body>
<span>测试数据01</span>
<div>

  <span>测试数据02</span>
  <p>
  <span>测试数据03</span>

  </p>
</div>
</body>
</html>